A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the United States Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
1. Field of the Invention
This invention relates to power supplies and in particular relates to power supplies for use with a variety of different devices.
2. Background of the Invention
Prior art power supplies include a variety of techniques, particularly those used for powering microelectronics such as the class of computers commonly known as xe2x80x9cnotebookxe2x80x9d computers such as the Powerbook Series available from Apple Computer of Cupertino Calif. and the Thinkpad Series available from International Business Machines (IBM) of Armonk, N.Y. More recently, even smaller personal computers referred to as xe2x80x9csub-notebooksxe2x80x9d have also been developed by various companies such as Hewlett-Packard""s Omnibook. The goal of these notebooks and sub-notebooks designs is to reduce the size and weight of the product. Currently, notebooks typically weigh about six pounds and sub-notebooks weigh slightly less than four pounds.
Many of these notebook and sub-notebook computers have a battery that must be recharged. Also, typically the computers are designed to be operated from external power sources such as line current and the electrical power system of automobiles.
To power these computers, the manufacturer typically provides an external power source. The external power source may be a switching power supply that may weigh close to a pound and may be about eight inches long, four inches wide and about four inches high. Smaller power supplies do exist but frequently they lack sufficient power to charge new batteries such as nickel hydride batteries.
Such external power supplies therefore contribute substantial additional weight that the user of the computer must carry with him or her to permit battery charging and/or operation from an electrical socket. Further, the external power supply is bulky and may not be readily carried in typical cases for such notebook and sub-notebook computers. In addition, conventional power supplies often have difficulty providing the necessary power curve to recharge batteries that have been thoroughly discharged. Also, a power supply is needed for each peripheral device, such as a printer, drive or the like. Thus, a user needs multiple power supplies.
While it has long been known to be desirable to reduce the size and weight of the power supply, this has not been readily accomplished. Many of the components such as the transformer core are bulky and have significant weight. Further, such power supplies may need to be able to provide DC power of up to seventy-five watts, thereby generating substantial heat. Due to the inherent inefficiencies of power supplies, this results in substantial heat being generated within the power supply. Reduction of the volume, weight and heat are all critical considerations for a power supply in this type of application and cannot be readily accomplished. In particular, it is believed to be desirable to have a package as thin as possible and designed to fit within a standard pocket on a shirt or a standard calculator pocket on a brief case. In addition, conventional power supplies are device specific and each device requires its own power supply. Therefore, users need multiple power supplies, which consumes space and increases unnecessary weight.
Cellular telephones are also extensive users of batteries. Typically, cellular telephone battery chargers have been bulky and are not readily transportable. Moreover, cellular telephone battery chargers often take several hours, or more, to charge a cellular telephone battery.
It is an object of an embodiment of the present invention to provide an improved small form factor power supply that is resistant to liquids and/or is programmable to supply power for a variety of different devices, which obviates for practical purposes, the above mentioned limitations.
These and other objects are accomplished through novel embodiments of a power supply having a transformer. The primary portion includes a primary rectifier circuit, a controller, first and secondary primary drive circuits each coupled magnetically by a coil to the core and a primary feedback circuit magnetically coupled by a separate core. The secondary portion includes a secondary output circuit magnetically coupled by a coil to the core that provides the regulated DC output and a secondary feedback back circuit magnetically coupled to the second core to provide a signal to the primary feedback circuit. In alternative embodiments, different transformer topologies may be used.
The controller provides a separate square wave signal to each of the two primary circuits and the phase of the square wave signals may be altered relative to each other as determined by the controller. The secondary circuit is positioned on the core relative to the two primary circuits so that the secondary circuit coil is positioned at a summing point on the core of the first and second primary circuit coils. The DC voltage and current levels produced at the output of the secondary circuit are monitored by the secondary feedback circuit to provide, through a secondary feedback coil and a primary feedback coil, a signal to the controller. The controller alters the phase between the signals driving the two coils to produce the desired output DC voltage and current at the secondary coils. This results in providing a regulated DC power supply with high efficiency.
By mounting all of the components on a printed circuit board using planar or low profile cores and surface mounted integrated circuits, a small form factor power supply can be attained. Given the high efficiency of the conversion and regulation, the system minimizes dissipation of heat permitting the entire power supply to be mounted within a high impact plastic container dimensioned, for example, as a right parallelepiped of approximately 2.85xc3x975.0xc3x970.436 inches, thereby providing a power supply that can readily be carried in a shirt pocket. It should be understood that changes in the overall dimensions may be made without departing from the spirit and scope of the present invention. Making a relatively thin package having relatively large top and bottom surface areas relative to the thickness of the package provides adequate heat dissipation.
Particular embodiments of the present invention utilize an improved transformer core that, by moving the relative position of the transformer legs, maximizes a ratio of the cross-sectional area of the transformer legs to the windings, thereby requiring less windings for the same magnetic coupling. Fewer windings means less area of a layer of a circuit board may be used so that the number of layers on the circuit board may be minimized. The improved transformer core also provides this maximized ratio while maintaining the ratio of the secondary and primary windings at a constant value. In alternative embodiments, different transformer topologies may be used.
It is an object of an additional embodiment of the present invention to alleviate the need for having a separate power supply for providing power for using each portable electronic device having distinct power requirements.
It is another object of the additional embodiment of the present invention to provide a power supply which is programmable to transmit an appropriate input power to any one of several electrically powered devices.
Briefly, the additional embodiment of the present invention is directed to a power supply which is programmable for providing between about zero and seventy five watts of power DC to a portable electronic appliance adapted for receiving DC power at one of an operational current and an operational voltage. The power supply comprises an input circuit for receiving input power from a power source, an output circuit adapted for coupling to the electronic appliance at an output connection for transmitting power to the electronic appliance and a power conversion circuit for providing output power at the operational current or the operational voltage in response to a detection of one of a programming signal received at the output connection.
The power supply may be configured to be programmable to support a variety of different devices and/or more than one device at a time. This may be accomplished with an on-board processor or by using external cables to provide the programming signal. Thus, the need for having multiple power supply devices (each adapted for meeting the power requirements of a distinct portable device) for providing power to different portable devices.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.